[PATCH] init: Initialize jump labels before command line option parsing

[Dan Williams <dan.j.williams@intel.com>]

When a module option, or core kernel argument, toggles a static-key it
requires jump labels to be initialized early. While x86, PowerPC, and
ARM64 arrange for jump_label_init() to be called before parse_args(),
ARM does not.

  Kernel command line: rdinit=/sbin/init page_alloc.shuffle=1 panic=-1 console=ttyAMA0,115200 page_alloc.shuffle=1
  ------------[ cut here ]------------
  WARNING: CPU: 0 PID: 0 at ./include/linux/jump_label.h:303
  page_alloc_shuffle+0x12c/0x1ac
  static_key_enable(): static key 'page_alloc_shuffle_key+0x0/0x4' used
  before call to jump_label_init()
  Modules linked in:
  CPU: 0 PID: 0 Comm: swapper Not tainted
  5.1.0-rc4-next-20190410-00003-g3367c36ce744 #1
  Hardware name: ARM Integrator/CP (Device Tree)
  [<c0011c68>] (unwind_backtrace) from [<c000ec48>] (show_stack+0x10/0x18)
  [<c000ec48>] (show_stack) from [<c07e9710>] (dump_stack+0x18/0x24)
  [<c07e9710>] (dump_stack) from [<c001bb1c>] (__warn+0xe0/0x108)
  [<c001bb1c>] (__warn) from [<c001bb88>] (warn_slowpath_fmt+0x44/0x6c)
  [<c001bb88>] (warn_slowpath_fmt) from [<c0b0c4a8>]
  (page_alloc_shuffle+0x12c/0x1ac)
  [<c0b0c4a8>] (page_alloc_shuffle) from [<c0b0c550>] (shuffle_store+0x28/0x48)
  [<c0b0c550>] (shuffle_store) from [<c003e6a0>] (parse_args+0x1f4/0x350)
  [<c003e6a0>] (parse_args) from [<c0ac3c00>] (start_kernel+0x1c0/0x488)

Move the fallback call to jump_label_init() to occur before
parse_args(). The redundant calls to jump_label_init() in other archs
are left intact in case they have static key toggling use cases that are
even earlier than option parsing.

Reported-by: Guenter Roeck <groeck@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 init/main.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/init/main.c b/init/main.c
index 598e278b46f7..7d4025d665eb 100644
--- a/init/main.c
+++ b/init/main.c
@@ -582,6 +582,8 @@ asmlinkage __visible void __init start_kernel(void)
 	page_alloc_init();
 
 	pr_notice("Kernel command line: %s\n", boot_command_line);
+	/* parameters may set static keys */
+	jump_label_init();
 	parse_early_param();
 	after_dashes = parse_args("Booting kernel",
 				  static_command_line, __start___param,
@@ -591,8 +593,6 @@ asmlinkage __visible void __init start_kernel(void)
 		parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
 			   NULL, set_init_arg);
 
-	jump_label_init();
-
 	/*
 	 * These use large bootmem allocations and must precede
 	 * kmem_cache_init()